Polymer stream transfer

Abstract

Process for heating a polymer-containing stream being transferred from a polymerization reactor to a separation zone or device, by passing the stream through at least two heaters operating in parallel, each heater having at least one transfer line for the stream and a heater for heating the transfer line. The average particle of the polymer is below 3 mm, the temperature of the polymer-containing stream at the outlet of all heaters is maintained above the dew point of the stream, and no heater has a volumetric flowrate of polymer-containing stream more than three times that of any other heater.

The invention claimed is: 
     
       1. Process for heating a polymer-containing stream being transferred from a polymerization reactor to a separation zone or device, comprising passing the stream through at least two heaters operating in parallel, each heater comprising at least one transfer line for the stream and heating means for heating the transfer line, wherein the average particle size of the polymer is below 3 mm, the temperature of the polymer-containing stream at the outlet of all heaters is maintained above the dew point of the stream, and no heater has a volumetric flowrate of polymer-containing stream more than three times that of any other heater. 
     
     
       2. Process for heating a polymer-containing stream being transferred from a polymerization reactor to a separation zone or device, comprising passing the stream through a heater comprising at least one transfer line for the stream and heating means for heating the transfer line, wherein the average particle size of the polymer is below 3 mm, and part of the polymer-containing stream from the polymerization reactor is diverted to a further heater also comprising at least one transfer line for the stream and heating means for heating the transfer line, either when the pressure drop across the first heater exceeds 50% of the total pressure drop between the reactor and the separation zone or device, or when the temperature of the polymer-containing stream at the heater outlet falls to less than 10° C. above the dew point temperature of the polymer-containing stream. 
     
     
       3. Process for heating a polymer-containing stream being transferred from a polymerization reactor which is increasing its production rate to a separation zone or device wherein the average particle size of the polymer is below 3 mm, which comprises a) passing the stream through a first heater or heaters each comprising a transfer line for the stream and heating means for heating the transfer line, and increasing the flow-rate of the stream whilst maintaining the temperature of the polymer-containing stream at the exit of each heater at least 10° C. above the dew point of the stream, and the temperature of the stream at any point along the length of the each transfer line below the softening point of the polymer, and then
 b) passing part of the stream from the polymerization reactor through an additional heater arranged in parallel to the first heater or heaters whilst maintaining the temperature of the polymer-containing stream at the exit of all heaters above the dew point of the stream, and the temperature of the stream at any point along the length of all transfer lines below the softening point of the polymer, said additional heater also comprising a transfer line for the stream and heating means for heating the transfer line. 
 
     
     
       4. Process for heating a polymer-containing stream being transferred from a polymerisation reactor to a separation zone or device wherein the average particle size of the polymer is below 3 mm, which comprises a) passing the stream through at least two heaters arranged in parallel and each comprising a transfer line for the stream and heating means for heating the transfer line, and the temperature of the stream at any point along the length of the each transfer line below the softening point of the polymer, and decreasing the flow-rate of the stream until the velocity at the exit of the heater falls below 30 m/s,
 and then b) shutting down one of the heaters and passing the stream only through the remaining heater or heaters. 
 
     
     
       5. Process according to  claim 2 , wherein part of the polymer-containing stream is diverted to a further heater when the pressure drop across the first heater exceeds 70% of the total pressure drop between the reactor and the separation zone. 
     
     
       6. Process according to  claim 2 , wherein part of the polymer-containing stream is diverted to a further heater when the temperature of the polymer-containing stream at the heater outlet falls to less than 10° C. above the dew point temperature of the polymer-containing stream. 
     
     
       7. Process according to  claim 3 , wherein the temperature of the polymer-containing stream at the exit of each heater is maintained at least 20° C. above the dew point of the stream. 
     
     
       8. Process according to  claim 3 , wherein the temperature of the polymer-containing stream at the exit of each heater is maintained at least 30° C. above the dew point of the stream. 
     
     
       9. Process according to  claim 1 ,  2 ,  3  or  4 , wherein in the case where at least two heaters are operating, the average stream velocity across any cross-section of each heater's transfer line is maintained between 2 and 100 m/s. 
     
     
       10. Process according to  claim 9 , wherein the average stream velocity across any cross-section of each heater's transfer line is maintained between 10 and 70 m/s. 
     
     
       11. Process according to  claim 1 ,  2 ,  3  or  4 , wherein in the case where at least two heaters are operating, the flow rate of a slurry in each transfer line is maintained at between 50% and 150%, of the average value of the flow rates in all the heaters in use. 
     
     
       12. Process according to  claim 11 , wherein the slurry flow rate in each transfer line is maintained at between 90% and 110% of the average value of the flow rates in all the heaters in use. 
     
     
       13. Process according to  claim 1 ,  2 ,  3  or  4 , wherein the average particle size of the solid polymer is less than 3 mm, the combined mass flowrate of the polymer-containing streams exiting all the heaters is no more than 15% greater than the mass flowrate exiting the reactor, and the average velocity of the polymer-containing stream either at a point 80% along the length of the heated part of each transfer line in use measured from the transfer line inlet, or at the transfer line outlet, is at least 6 m/s. 
     
     
       14. Process according to  claim 13 , wherein the average velocity of the polymer-containing stream either at a point 80% along the length of the heated part of each transfer line in use measured from the transfer line inlet, or at the transfer line outlet, is at least 8 m/s. 
     
     
       15. Process according to  claim 13 , wherein the average velocity of the polymer-containing stream either at a point 80% along the length of the heated part of each transfer line in use measured from the transfer line inlet, or at the transfer line outlet, is at least 10 m/s. 
     
     
       16. Process according to  claim 1 ,  2 ,  3  or  4 , wherein the average velocity of the polymer-containing stream at 80% along the length of the heated part of each transfer line in use, measured from the transfer line inlet, is equal to or greater than its average velocity at 20% along the length of the heated part of the transfer line. 
     
     
       17. Process according to  claim 1 ,  2 ,  3  or  4 , wherein the sum of the mass flowrates of the polymer-containing streams exiting all of the heaters is substantially the same as the mass flowrate exiting the reactor. 
     
     
       18. Process according to  claim 1 ,  2 ,  3  or  4 , wherein the ratio of the average velocity of the polymer-containing stream at 80% along the length of the heated part of each transfer line in use to its average velocity at 20% along the length of the heated part of the transfer line is greater than 1.1. 
     
     
       19. Process according to  claim 18 , wherein the ratio of the average velocity of the polymer-containing stream at 80% along the length of the heated part of each transfer line in use to its average velocity at 20% along the length of the heated part of the transfer line is greater than 1.3. 
     
     
       20. Process according to  claim 1 ,  2 ,  3  or  4 , wherein the average velocity of the polymer-containing stream at 60% along the length of the heated part of each transfer line in use measured from the transfer line inlet is equal to or greater than its average velocity at 20% along the length of the heated part of the transfer line. 
     
     
       21. Process according to  claim 1 ,  2 ,  3  or  4 , wherein the ratio of each transfer line's diameter 80% along its heated length, D 80 , to the diameter 20% along its heated length, D 20 , is greater than 1. 
     
     
       22. Process according to  claim 21 , wherein the ratio of each transfer line's diameter 80% along its heated length, D 80 , to the diameter 20% along its heated length, D 20 , is greater than 1.2. 
     
     
       23. Process according to  claim 21 , wherein the ratio of each transfer line's diameter 80% along its heated length, D 80 , to the diameter 20% along its heated length, D 20 , is greater than 1.3. 
     
     
       24. Process according to  claim 1 ,  2 ,  3  or  4 , wherein the temperature of the internal surface of each transfer line from 50% to 100% along its heated length is maintained below the softening point of the polymer. 
     
     
       25. Process according to  claim 23 , wherein the temperature of the internal surface of each transfer line along all of its heated length is maintained below the softening point of the polymer. 
     
     
       26. Process according to  claim 1 ,  2 ,  3  or  4 , wherein the heat input to the polymer-containing stream is adjusted by changing the temperature of the heating medium in contact with the outer surface, and/or by changing the size of the heated area of the transfer line. 
     
     
       27. Process according to  claim 1 ,  2 ,  3  or  4 , wherein the pressure drop across each transfer line in use per unit length is between 0.01 bar/m and 0.2 bar/m. 
     
     
       28. Process according to  claim 27 , wherein the pressure drop across each transfer line in use per unit length is between 0.0125 bar/m and 0.1 bar/m. 
     
     
       29. Process according to  claim 27 , wherein the pressure drop across each transfer line in use per unit length is between 0.0125 bar/m and 0.04 bar/m.